Ignition and reignition issues with the batteries in electric vehicles are also concerns for energy storage systems. BY JESSE ROMAN

ONE OF THE MORE PECULIAR and least-understood hazards that ESS can present occurs in the lithium-ion family of batteries, which are also used in electric vehicles. Like trick birthday candles, lithium-ion batteries have shown they can ignite, or reignite, long after they have been damaged or involved in a fire—hours, days, or even weeks later. In 2011, for example, the lithium-ion battery of a Chevy Volt caught fire three weeks after it was damaged in a side-impact crash test conducted by the National Highway Transportation Safety Administration.

The Chevy Volt following its side-impact test in 2011, after the fire, and the car's lithium-ion battery. ​Photograph: National Highway Traffic Safety Administration

In 2013, the Fire Protection Research Foundation undertook a research project to examine emergency response in incidents involving electric vehicle batteries. As part of the scope, researchers looked at how lithium-ion batteries in electric vehicles respond in a fire. In each of the six full-scale burn tests, firefighters at the test site found that they needed to flow large amounts of water on the batteries, because fire kept flaring up even after it appeared to be extinguished. In one test, a battery fire reignited 22 hours after it was thought to be extinguished. “Everything looked normal,” recalled Andrew Blum, a researcher at the firm Exponent, which conducted the tests. “When we looked at the battery through a thermal imager, everything was back to ambient temperatures; the fire was extinguished as we would define it. But there was something going on internally in the module, and we just couldn’t tell.” In two of the tests, firefighters ran out of air and had to switch tanks because of the length of time it took to fully extinguish the battery, according to Blum.

The problem raises many questions. How are firefighters to know when a fire involving these batteries is actually extinguished? How long do they need to wait to declare a scene safe, especially for a battery located, for example, on an upper floor of a residential high-rise? What are the liability concerns? The staffing and equipment needed to deal with a prolonged fire with reignitions might also be a challenge for some fire departments. “We may need manpower there to keep an eye on these things,” Blum said. “I don’t think anybody wants to start ripping out batteries from a building two hours after a fire. Where would you put them?”

Lt. Paul Rogers, a hazardous materials expert with the Fire Department of New York (FDNY), offered a compact assessment of the lithium-ion reignition issue. “We have more questions than answers—I’m not sure how we are going to handle that right now.”

​JESSE ROMAN is staff writer for NFPA Journal. He can be contacted at jroman@nfpa.org. Top Photograph: National Highway Traffic Safety Administration